1. Field of the Invention
The present invention relates to an aqueous dispersion for chemical mechanical polishing (hereunder referred to as xe2x80x9caqueous dispersionxe2x80x9d) and to a chemical mechanical polishing process. More specifically, the invention relates to an aqueous dispersion capable of efficient polishing of various types of working films formed on semiconductor substrates, which allows free adjustment of the polishing rate ratios for copper films, barrier metal films and insulating films, and which can give adequately flattened and high precision finished surfaces, as well as to a chemical mechanical polishing process employing the aqueous dispersion. The aqueous dispersion of the invention is particularly useful for the second-stage chemical mechanical polishing step of two-stage polishing processes, or for the second-stage or third-stage chemical mechanical polishing step of three-stage polishing processes.
2. Description of the Prior Art
A recent technique used in the manufacture of semiconductor devices is a process whereby a hole or groove is formed in an insulating film on a processing wafer, and then a barrier metal film made of a hard metal or the like is formed and a wiring material such as tungsten, aluminum or copper is embedded in the hole or groove to form a wiring material film, after which the unnecessary portions of the wiring material film and barrier metal film are removed by chemical mechanical polishing (hereunder referred to as xe2x80x9cCMPxe2x80x9d) to complete the wiring. The wiring formed by this technique is known as damascene wiring.
It is common to form damascene wiring by a CMP process comprising a plurality of CMP steps.
For example, in a CMP process comprising two CMP steps (hereunder referred to as xe2x80x9ctwo-stage polishing processxe2x80x9d), the wiring material such as copper is polished mainly in the first-stage CMP step, and the barrier metal film is polished mainly in the second-stage CMP step. Several forms of the two-stage polishing process have been proposed, and a great number of aqueous dispersions for use in each stage have also been proposed.
First two-stage polishing process involves polishing in the first-stage CMP step until the copper is almost completely removed, and then removing just the barrier metal film in the second-stage CMP step. In this case, dishing often occurs in the wiring sections during the first-stage CMP step, and this dishing cannot be corrected by the second-stage CMP step in which mainly the barrier metal film is polished, and therefore it is sometimes difficult to form satisfactory damascene wiring.
Second two-stage polishing process that has been proposed involves incomplete removal of the copper in the first-stage CMP step to an extent that does not cause dishing in the wiring sections, and removal of the copper remaining from the first-stage CMP step with the barrier metal film in the second-stage CMP step. This process sometimes results in inadequate smoothness of the finished surface, and requires a longer time to complete the polishing, thus also leading to the problem of increased costs.
In the first and second processes mentioned above, different polishing performance is required for the aqueous dispersions used in the second-stage CMP step, and therefore different aqueous dispersions with different component contents are used for the second stages, respectively.
In manufacturing processes for semiconductor devices, insufficient flatness of the underlayer wiring can cause unwanted irregularities on the surface of the insulating film, and the copper film and barrier metal film formed over those irregularities often create xe2x80x9cwavinessxe2x80x9d. As a measure against such situations, it has been proposed to employ a polishing process with three CMP steps (hereunder referred to as xe2x80x9cthree-stage polishing processxe2x80x9d) in order to eliminate the waviness and obtain a flatter finished surface. The third-stage CMP step uses an aqueous dispersion whose components and composition are suited for that step.
In the various CMP steps described above, however, it is not easy to accomplish efficient polishing of barrier metal films made of metals with high hardness, such as tantalum. On the other hand, since copper films are relatively soft they are easy to polish and can produce dishing, sometimes preventing a flat finished surface. Wiring breaks also sometimes occur due to scratching and the like.
When the polishing surface is a porous insulating film with a low dielectric constant, it is difficult to achieve an adequate polishing rate if an aqueous dispersion with a low pH is used for the CMP, and conversely if the pH is high, the insulating film is excessively polished making it difficult to form satisfactory damascene wiring. It also becomes difficult to prevent scratches during the CMP of porous insulating films with low dielectric constants.
[Problems to be Solved by the Invention]
It is an object of the present invention to provide an aqueous dispersion for chemical mechanical polishing that can give sufficiently flattened and highly precise finished surfaces and can form satisfactory damascene wiring, as well as a chemical mechanical polishing process employing the aqueous dispersion.
It is another object of the invention to provide an aqueous dispersion for chemical mechanical polishing that can efficiently polish both copper films and barrier metal films, which can give sufficient flattened finished surfaces without excessive polishing of insulating films, and which can form satisfactory damascene wiring, as well as a chemical mechanical polishing process employing the aqueous dispersion.
[Features of the Invention]
We studied polishing of working films formed on semiconductor substrates with the object of obtaining an aqueous dispersion for chemical mechanical polishing capable of sufficiently flattening finished surfaces.
As a result, it was discovered that finished surfaces which are sufficiently flattened with high precision can be obtained by polishing of a copper film, barrier metal film and an insulating film under the same conditions if the aqueous dispersion used for the CMP has a specific value for the polishing rate ratio for each film.
It was further discovered that by using an aqueous dispersion with a specific composition containing a heterocyclic compound, an organic acid, an oxidizing agent and if necessary a surfactant, it is possible to easily adjust the polishing rate ratios for the copper film, barrier metal film and insulating film, and to efficiently polish the copper film and barrier metal film while giving a sufficiently flattened and highly precise finished surface with no excessive polishing of the insulating film.
The present invention has been accomplished on the basis of these discoveries.
In other words, the aforementioned problems are solved by the present invention which provides an aqueous dispersion for chemical mechanical polishing and a chemical mechanical polishing process having following constitutions.
[1] An aqueous dispersion for chemical mechanical polishing characterized in that, for polishing of a copper film, barrier metal film and insulating film under the same conditions, the ratio (RCu/RBM) of the polishing rate for said copper film (RCu) and the polishing rate for said barrier metal film (RBM) is such that 0.5xe2x89xa6RCu/RBMxe2x89xa62, and the ratio (RCu/RIn) of the polishing rate for said copper film (RCu) and the polishing rate for said insulating film (RIn) is such that 0.5xe2x89xa6RCu/RInxe2x89xa62.
[2] An aqueous dispersion for chemical mechanical polishing according to [1] above, wherein said barrier metal film is composed of tantalum and/or tantalum nitride.
[3] An aqueous dispersion for chemical mechanical polishing according to [1] above, which contains at least an abrasive, water and a polishing rate adjusting component.
[4] An aqueous dispersion for chemical mechanical polishing according to [3] above, wherein said abrasive consists of at least one type of particles selected from among inorganic particles, organic particles and inorganic/organic composite particles.
[5] An aqueous dispersion for chemical mechanical polishing according to [3] above, wherein said polishing rate adjusting component is maleic acid ion.
[6] An aqueous dispersion for chemical mechanical polishing according to [5] above, wherein the concentration of said maleic acid ion is 0.005-1 mole/liter.
[7] An aqueous dispersion for chemical mechanical polishing according to [1] above, wherein the pH is 7-11.
[8] An aqueous dispersion for chemical mechanical polishing characterized in that it contains an abrasive, a heterocyclic compound, an organic acid and an oxidizing agent, and for polishing of a copper film, barrier metal film and insulating film under the same conditions, the ratio (RCu/RBM) of the polishing rate for said copper film (RCu) and the polishing rate for said barrier metal film (RBM) is such that 0 less than RCu/RBMxe2x89xa65, and the ratio (RIn/RBM) of the polishing rate for said insulating film (RIn) and the polishing rate for said barrier metal film RBM is such that 0 less than RIn/RBMxe2x89xa62.
[9] An aqueous dispersion for chemical mechanical polishing according to [8] above, which further contains a surfactant at 0.0001-0.1 wt %.
[10] An aqueous dispersion for chemical mechanical polishing according to [8] above, wherein the pH is below 8.5, said ratio RCu/RBM is such that 0.5 less than RCu/RBMxe2x89xa65, and said ratio RIn/RBM is such that 0 less than RIn/RBMxe2x89xa60.1.
[11] An aqueous dispersion for chemical mechanical polishing according to [10] above, wherein said heterocyclic compound is either or both quinaldinic acid or 7-hydroxy-5-methyl-1,3,4-triazaindolizine.
[12] An aqueous dispersion for chemical mechanical polishing according to [10] above, which further contains a surfactant at 0.0001-0.1 wt %.
[13] An aqueous dispersion for chemical mechanical polishing according to [8] above, wherein the pH is 8.5 or above, said ratio RCu/RBM is such that 0 less than RCu/RBMxe2x89xa60.1, said ratio RIn/RBM is such that 0 less than RIn/RBMxe2x89xa60.1, and which further contains a surfactant at 0.0001-0.1 wt %.
[14] An aqueous dispersion for chemical mechanical polishing according to [13] above, wherein said heterocyclic compound is benzotriazole.
[15] An aqueous dispersion for chemical mechanical polishing according to [8] above, wherein the pH is 8.5 or above, said ratio RCu/RBM is such that 0 less than RCu/RBMxe2x89xa60.05, and said ratio RIn/RBM is such that 0.1 less than RIn/RBMxe2x89xa62.
[16] An aqueous dispersion for chemical mechanical polishing according to [15] above, wherein said heterocyclic compound is at least one from among benzotriazole, quinaldinic acid and 7-hydroxy-5-methyl-1,3,4-triazaindolizine.
[17] A chemical mechanical polishing process characterized by comprising
a first stage of chemical mechanical polishing which employs an aqueous dispersion for chemical mechanical polishing with a ratio (RCu/RBM) of the polishing rate for copper films (RCu) and the polishing rate for barrier metal films (RBM) of 20 or greater, and
a second stage of chemical mechanical polishing which employs an aqueous dispersion for chemical mechanical polishing according to any one of [1] to [7] above.
[18] A chemical mechanical polishing process characterized in that the second stage of chemical mechanical polishing of a polishing process comprising two stages of chemical mechanical polishing is carried out using an aqueous dispersion for chemical mechanical polishing according to any one of [10] to [16] above.
[19] A chemical mechanical polishing process characterized in that the second stage of chemical mechanical polishing of a polishing process comprising three stages of chemical mechanical polishing is carried out using an aqueous dispersion for chemical mechanical polishing according to any one of [10] to [12] above.
[20] A chemical mechanical polishing process characterized in that the third stage of chemical mechanical polishing of a polishing process comprising three stages of chemical mechanical polishing is carried out using an aqueous dispersion for chemical mechanical polishing according to any one of [13] to [16] above.
[Effect of the Invention]
The aqueous dispersion of the invention according to claims 1 to 7 has a specific ratio between the polishing rates for copper films and barrier metal films and a specific ratio between the polishing rates for copper films and insulating films, thus allowing working films to be polished to the same degree at suitable rates while producing no scratches or dishing, so that the dispersion is useful for manufacture of semiconductor devices.
According to the CMP process of the invention as described in claim 17, an aqueous dispersion according to the invention as described in any of claims 1 to 7 is used to obtain finished surfaces with sufficient flatness and high precision.
According to the aqueous dispersion of the invention as described in claims 8 to 16, the composition of the aqueous dispersion may be changed to allow easy adjustment of the polishing rate ratio between the copper film, barrier metal film and insulating film. This allows the barrier metal film to be polished with adequate efficiency, and offers an aqueous dispersion for CMP that does not excessively polish the insulating film. The aqueous dispersion, as described in claims 18 to 20, is useful for the second stage of a two-stage polishing process, or for the second stage or third stage of a three-stage polishing process in the manufacture of semiconductor devices.
Such easy adjustment of the polishing rate ratio by changing the composition is preferred because it requires no complicated apparatuses or complex procedures at the aqueous dispersion supply end. It is also preferred because the demand end only needs to store the suitable and necessary amounts of aqueous dispersions for each polishing, and the storage volume can therefore be reduced.